Chemical reduction of nitro compounds to purify alpha, omage alkanedioic acid esters



nitcd States Patgm Q CHEMICAL REDUCTION OF NITRO COMPOUNDS TO PURIFY :,w ALKANEDIOIC ACID ESTERS Norman C. Hill, Akron, Ohio, and Vincent P. Kuceski, Park Forest, Ill., assignors to The C. P. Hall Company, Akron, Ohio, a corporation of ()hio No Drawing. Application August 18, 1954 Serial No. 450,821

3 Claims. (Cl. 260-482) This invention relates to the oxidation of saturated and unsaturated, cyclic and acyclic, aliphatic hydrocarbons and oxygenated derivatives thereof, by nitric acid, nitrous acid or an oxide of nitrogen higher than N 0, and the production of carboxylic acids therefrom. More particularly, the invention relates to the chemical reduction of nitrogen compounds formed in such oxidation reactions.

The starting material may be found in nature or may be made synthetically and must contain 4 or more adjacent carbon atoms in a saturated chain. It may be fatty acid, such as red oil, stearic acid, or fatty acid of vegetable origin such as cocoanut fatty acid, cottonseed fatty acid and fatty acid from other seed oils. The starting material may be derived from petroleum materials or be synthesized as in the FischenTropsch reaction. For instance, it may be one or more of the alcohols, aldchydes, ketones, monocarboxylic acids, esters or others produced in such syntheses. Other materials such as paraflinic and olefinic hydrocarbons present in or derived from petroleum or obtained by the cracking of carbonaceous'materials, etc. may be used. The oxidation of materials derived by the Oxo process and by the Fischer- Tropsch process is described in Hill application Serial No. 277,077 which has matured into U. S. Patent 2,768,201. This process involves treating residues from such operations with nitric acid, with or without admixture with air, at elevated temperatures and superatmospheric pressures, and the production of carboxylic acids thereby. The oxidation of the other materials has been described in the literature.

In the oxidation, the nitric acid or other oxidizing agent may be used alone or in conjunction with air or oxygen. It may be preceded or followed by other oxidations such as ozonization, etc.

It has been found in the oxidation of these starting materials that nitrogen derivatives have been formed, a large proportion of them being nitro compounds. The nitrogen may add onto any one of various places in the chain. One or more carboxylic groups may be formed. The process has particular application to the treatment of the oxidation products derived from a fatty acid in which monoand dicarboxylic acids are produced. During the oxidation of a fatty acid and the production of monocarboxylic acids and dicarboxylic acids, objectionable side reactions occur in which the nitrogen attaches itself to the chain to form a primary or secondary nitro compound or nitrite or nitrate.

The object of the invention is to chemically reduce such nitrogen-containing materials, regardless of the starting material. Generally the reduced products are then separated from the carboxylic acid. Such reduction is preferably accomplished by first converting the carboxylic acid to an ester, under suitable conditions, but may be carried out in the presence of the carboxylic acid.

The nature of the nitrogen-containing compounds depends upon the starting material and the conditions of the reaction. If the starting material contains hydro- 'ice carbon, the nitrogen may add to the hydrocarbon chain without conversion of any carbon of the chain to a carboxylic group. For purposes of illustration, the treatment of a dicarboxylic acid to which the nitrogen group has been added is considered. The acid has been converted to the diester. in the formulae shown below, the dicarboxylic acid is represented as being of any given chain length, the letters in and n being zero or an integer, with a chain length of at least 4 carbon atoms. Thus, the nitrogen may attach itself to a carbon adjacent to a carboxylic group or to another non-terminal carbon atom.

in the compound illustrated in the foregoing, X may be nitroso (-NO), nitro (-M0 hydroxyl amine (Ni-10H), or azo -N=N-), or any other carbon nitrogen bonded compounds. Such a carbon-nitrogen compound can be reduced by chemical or catalytic reduction to the amine, and the amine may be removed by an aqueous acid wash. The Wash may be a mineral or organic acid. The following general classes of reactions illustrate types that may be used. for the reduction.

(A) The carbon-nitrogen compound can. be reduced with a metal and an acid, as, for example, zinc dust and an alcoholic solution of a mineral acid such as hydrochloric acid.

(B) Or by catalytic reduction with Raney nickel or with reduced precipitated nickel. This would include reduced nickel carbonate or reduced nickel hydrate or reduced nickel formate.

(C) Or the chemical reduction may be carried out by catalytic reduction with platinum or palladium.

insofar as such reductions do not produce objection able soaps such as zinc or. nickel soaps or other objectional side reactions, such reductions may be carried out in the presence of the carbcxylic acids without prior conversion to esters, and process C above lends itself particularly to such an operation.

The amines thus formed need not be separated from the carboxylic acid or the ester. They are stable compounds and for some uses such productsv are not objectionable. On the other hand, they may be separated from the esters by washing with an aqueous solution of a mineral acid or suitable acid such as acetic acid, and if present in the carboxylic acid may be similarly removed after esterification of the acid.

if process A above is followed, mineral acid used as a source of hydrogen may be present in such amount as to render the resulting amine water soluble.

in the following formula, Y represents nitrite (-ONO) or nitrate (-ONO COO.All-: COO.Alk

(6112). ((3112),; H-Y -011 2)" (CH2) COQAlk 000.1111:

Such compounds on reduction produce alcohols as illustrated. The alcohols are relatively stable and are not harmful in the esters or acids.

As illustrative of the invention without limiting the invention, the following example is given:

Red oil is converted to carboxylic acid by oxidation with nitric acid of 25 percent concentration at C. for three hours. The conversion is 32.5 percent to dicarboxylic acids. The acids obtained by such a reaction analyzed:

After the crystalline dicarboxylic acids are removed from the aqueous nitric acid, the dicarboxylic acids remaining in the mother liquor have the following composition:

22.93 0 23.90 0 16.82 0 22.75 c 4.71 c -r 5.73 01 3.08

These acids in the mother liquor (on the dry basis) analyze about 1 percent nitrogen. On conversion to the diester the diester mixture analyzed 0.84 percent of nitrogen.

As an example of chemical reduction, this diester was dissolved in methyl alcohol containing 5 percent by weight of sulfuric acid. To the unheated, well-stirred mixture was added zinc dust in small increments until 5 percent by weight of the Original ester was added. The reduction took place over a period of two hours. At the end of the two hours, the mixture was diluted with ten times its volume of water and the ester layer separated, washed with water and dried. The ester thus obtained was analyzed and showed the presence of only 0.008 percent nitrogen.

Thus, the ester was substantially entirely free from nitrogen-containing derivatives.

Alternatively, the ester may be treated for catalytic reduction by methods which are well known to the man skilled in the art.

The dicarboxylic acids to which the specification refers are designated in the claims by the expression alpha, omega-alkanedioic acids.

The invention is not limited to the foregoing example, but is defined in the claims which follow:

What we claim is:

1. In the process of producing dialkyl esters of alpha, omega-alkanedioic acids obtained by esterifying such acids produced by oxidizing with an oxidizing agent from the class consisting of nitric acid, nitrous acid and oxides of nitrogen higher than N 0, a material of the class consisting of saturated and unsaturated cyclic and acyclic aliphatic hydrocarbons and oxygenated derivatives thereof which contain at least 4 carbon atoms in a saturated chain, some but not all of which alpha, omega-alkanedioic acid is substituted with at least one reducible nitrogencontaining substituent, the steps which comprise reducing said nitrogen-containing substituent of the dialkyl ester to an amino group and with acid producing a watersoluble nitrogen-containing acid salt, and then separating said acid salt from the unsubstituted dialkyl ester by solution into an aqueous solution.

2. In the process of treating a mixture of dialkyl esters of alpha, omega-alkanedioic acids and carboxylic acid with a reducible nitrogen-containing substituent obtained by oxidizing with aqueous nitric acid a fatty acid obtained from a seed oil, the steps which comprise esterifying the mixture to obtain dialkyl esters of the alpha, omegaalkanedioic acids and alkyl ester of said carboxylic acid with the nitrogen-containing substituent, reducing said nitrogen-containing substituent to an amino group and acidifying the mixture whereby the amino-substituted carboxylic acid is converted to a water-soluble acid salt, and then separating said acid salt from the dialkyl ester of the alpha, omega-alkanedioic acid by solution in an aqueous medium.

3. The method of separating carboxylic acid with a reducible nitrogen-containing substituent from a mixture of alpha, ornega-alkanedioic acids having 4 to 10 carbon atoms, which method comprises esterifying the alpha, omega-alkanedioic acids to dialkyl esters and the aforesaid substituted carboxylic acid to an alkyl ester thereof; then subjecting the esterified mixture to reduction to convert the alkyl ester of the substituted carboxylic acid to an alkyl ester of an amino carboxylic acid and acidifying and treating with an aqueous medium whereby a water-soluble acid salt is formed from the substituted carboxylic acid ester and it is dissolved into the aqueous medium and thereby separated from the dialkyl esters.

References Cited in the file of this patent UNITED STATES PATENTS 2,203,680 Ellingboe June 11, 1940 2,560,156 Cavanaugh et al. July 10, 1951 2,570,297 Weisblat et al Oct. 9, 1951 2,599,653 Moe et al. June 10, 1952 2,716,133 Pooler Aug. 23, 1955 FOREIGN PATENTS 695,170 Great Britain Aug. 5, 1953 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,831,883 Norman 00 Hill et al0 April 222, 1958 It is hereby certified that error appears .in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 21 for the nitro group "M0 read m N02 u Signed and sealed this 24th day of June 1958,,

(SEAL Attest: KARL H, AXLINE ROBERT C. WATSON Attestlng Officer Commissioner of Patents 

1. IN THE PROCESS OF PRODUCING DIALKYL ESTERS OF ALPHA, OMEGA-ALKANEDIOILIC ACIDS OBTAINED BY ESTERIFYING SUCH ACIDS PRODUCED BY OXIDIZING WITH AN OXIDIZING AGENT FROM THE CLASS CONSISTING OF NITRIC ACID, NITROUS ACID AND OXIDES OF NITROGEN HIGHER THAN N2O, A MATERIAL OF THE CLASS CONSISTING OF SATURATED AND UNSATURATED CYCLIC AND ACYCLIC ALIPHATIC HYDROCARBONS AND OXYGENATED DERIVATIVED THEREOF WHICH CONTAIN AT LEAST 4 CARBON ATOMS IN A SATURATED CHAIN, SOME BUT NOT ALL OF WHICH ALPHA, OMEGA-ALKANEDIOIC ACID IS SUBSTITUTED WITH AT LEAST ONE REDUCIBLE NITROGENCONTAINING SUBSTITUENT, THE STEPS WHICH COMPRISE REDUCING SAID NITROGEN-CONTAINING SUBSTITUENT OF THE DIALKYL ESTER TO AN AMINO GROUP AND WITH ACID PRODUCING A WATERI SOLUBLE NITROGEN-CONTAINING ACID SALT, AND THEN SEPARATING SAID ACID SALT FROM THE UNSUBSTITUTED DIALKYL ESTER BY SOLUTION INTO AN AQUEOUS SOLUTION. 